RU2459072C1 - Method of hydraulic fracturing of low-permeable formation of injection well - Google Patents

Abstract

FIELD: oil and gas production. ^ SUBSTANCE: method includes pumping of hydraulic fracturing fluid into formation through the well via tubing with packer with viscosity not less than 0.01 Pas with the following pumping of hydraulic mixture with proppant. Hydraulic fracturing is done by intervals from the top downwards in each interlayer of formation with the use of two packers mounted above and below the formation interval specified for hydraulic fracturing. Each adsorbing interlayer of formation is pumped via tubing by hydraulic fracturing fluid under pressure twice exceeding the injection capacity of formation for 3-4 hours. The above operations are repeated depending upon the quantity of formation adsorbing interlayers. The packing of all adsorbing interlayers of formation is done by pumping hydraulic mixture with proppant via tubing by installation of blind packer under the lower adsorbing interlayer and through packer in tubing over the upper interlayer of formation, the hydraulic mixture - lime slurry - is pumped into the well from 3 to 6 m3 in concentration 20 kg of CaO per 1 m of water with the following adding of spent sulphite liquor in ratio from 1:0.2 to 1:0.4 with viscosity 450-500-10-3 Pas. After that the injection well is put into operation. As working agent pumped into injection well there used is water of 1000-1180 kg/m density not containing suspended solid particles and ferrous hydroxide. ^ EFFECT: increase of method efficiency not depending upon interlayer injection capacity and speed of hydraulic fracturing fluid pumping into formation as well as the possibility to perform repetitive operations on formation injection capacity restoration. ^ 2 dwg

Description

The invention relates to the field of hydraulic fracturing in low-permeable formations and can find application, in particular, in oil and gas fields.

A known method of hydraulic fracturing (patent RU No. 2122633, IPC 8 E21B 43/27, publ. 1998), which includes injecting into the formation at a pressure above the fracturing pressure of acid agents and proppant.

This method does not allow to develop injection wells in clay reservoirs and low-power sandstones for injection.

A method of hydraulic fracturing (Fracturing) is also known (patent RU No. 2109935, IPC 8 E21B 43/26, published in Bulletin No. 16 of 04/27/1998) by pumping fracturing fluid into the reservoir with injection as the first portion of fluid with colmatizing additives, which use a stabilized clay oil-water suspension, which is pumped in an amount sufficient to clog the cracks and restore the tightness of the annular cement stone, at a pressure of up to 0.9 from the calculated fracturing pressure, and stabilized clay oil-water This suspension was used with the addition of iron oxide in an amount of 100-200 kg / m, a stable carboxymethylcellulose in an amount of 0.45-0.55% by volume, the clay stabilized water-in-suspension is pumped in a predetermined volume.

The disadvantage of this method is the need to use high-pressure expensive pumping equipment, since batch injection of fracturing fluids occurs at high discharge pressures, the process is long and labor-intensive, and its use in a low-permeable formation has low efficiency.

The closest in technical essence is the method of hydraulic fracturing of an impermeable underground formation (patent RU No. 2402679, IPC 8 E21B 43/26, published in Bulletin No. 30 dated October 27, 2010), which includes injecting hydraulic fracturing fluid containing proppant particles through a well in the fracture created in the underground reservoir, while the injection process provides a turbulent mode of fluid flow in the fracture by pumping a fracturing fluid with a viscosity of less than 0.01 Pa · s with an injection rate of at least 8 m ³ / min, and the fluid contains proppant particles, ra MIS - σ are determined by calculation, and the pre-injection is performed in the well a low viscosity fracturing fluid containing no proppant, and after pumping a fracturing fluid with proppant particles in the fracture with proppant slurry is pumped coated rubber sheath.

The disadvantages of this method are:

- firstly, low efficiency (up to 20-30%) of application, due to the fact that in low-permeable formations of injection wells with clay interlayers alternating with permeable sandstones with a small total thickness and low permeability, the specific injectivity is less than 0.1 m ³ / (days × MPa);

- secondly, the limited use, because low-permeability formations of injection wells often have low injectivity, and it is almost impossible to achieve a hydraulic fracturing fluid injection rate of 8 m ³ / min or more during hydraulic fracturing;

- thirdly, after hydraulic fracturing, the injectivity of a low-permeability layer of an injection well decreases rapidly and after 2-3 months, repeated work is carried out to restore it, so the requirements for injected water become especially stringent for such formations.

An object of the invention is to increase the efficiency of hydraulic fracturing in low-permeable formations with the possibility of applying the method in low-permeable formations, regardless of the injectivity of the formation and the rate of injection of hydraulic fracturing fluid into the formation during hydraulic fracturing and increasing the period of operation of the well until loss of injectivity of the low-permeable formation and, accordingly, repeated work to restore the injectivity of the reservoir.

The problem is solved by the method of hydraulic fracturing of a low-permeable layer of an injection well, including pumping tubing through a well with a packer into the formation of hydraulic fracturing fluid with a viscosity of less than 0.01 Pa · s, followed by pumping a hydraulic mixture with proppant.

New is that hydraulic fracturing is performed from top to bottom in each interlayer with the use of two packers installed above and below the interval intended for hydraulic fracturing, and hydraulic fracturing is injected into each absorbing interlayer through a tubing string for 3-4 hours under pressure, twice the injectivity pressure of the underground formation, the above operations are repeated depending on the number of absorbing interlayers of the formation, and then installing a blank packer under the lower absorbing m layer and a through packer in the tubing string above the upper layer of the formation compaction of all absorbing layers of the formation by pumping through the tubing string a proppant slurry, which is used to pump from 3 to 6 m ^{3 of} lime suspension in a concentration of 20 kg CaO per 1 m ³ water, followed by addition in a ratio of 1: 0.2 to 1: 0.4 sulfite-alcohol stillage (PRS) with a viscosity of 450-500 · 10 ^-3 Pa · s, after which the injection well is put into operation, and as a working agent injected into the injection well using water density 1000-1180 kg / m ^3, not containing slurry, and iron hydroxide.

In figures 1 and 2 schematically shows the sequence of the proposed method.

The essence of the method is as follows.

Injection well 1 (see figure 1), revealed the formation 2 with clay interlayers (impermeable layers) 3 '; 3 '' ... 3 '', alternating with permeable sandstones (absorbing interlayers) 4 '; 4 '' ... 4 '' with a small total thickness and low permeability. The specific injection rate of the formation 2 is less than 0.1 m ³ / day × MPa). The development of such wells for injection is delayed for several months and requires the use of the most effective methods of influencing their bottom-hole zone. The injectivity of the well 1 decreases rapidly and after 2-3 months they are again being restored.

However, in the horizons represented by the alternation of clays and sandstones, hydraulic fracturing of formation 2 is ineffective, since cracks form in one of the most permeable absorbing layers, for example 4 '' formation 2. The best results are obtained with interval fracturing, i.e. successive hydraulic fracturing of each absorbent interlayer 4 '; 4 '' ... 4 '' of formation 2. In this case, descent on the tubing string 5 of two packers 6, installed above and below the interval intended for processing, for example, the absorbing layer 4 ', is necessary (see Fig. 1).

As two packers 6 for conducting the interval hydraulic fracturing, for example, a design developed by the TatNIPIneft institute can be used - a device for treating formations in a well (patent RU No. 2282710 IPC 8 E21v 33/12, published in bulletin No. 24 dated 08.27.08 .2006). It consists of the main and additional packers lowered into the borehole on the tubing string, respectively, with mechanical and hydraulic anchors interconnected by means of a disconnector and a pipe (shown in figure 1 conditionally). The length of the pipe L should be not less than the height of the absorbing interlayer of the low-permeable formation, for example, 4 'of the hydraulic fracturing.

If the takeoff between the heights of the absorbing interlayers, for example, 4 'and 4' 'of formation 2 is small, for example 1 m and 1, 5 m, and the heights of clay impermeable layers 3', 3 '' and 3 '' 'are 2 meters, which allows hermetically cut off one or another interval of the absorbing layers of the formation from each other during hydraulic fracturing, then unpack the device, lower the tubing string down and make the device for hydraulic fracturing in the next interval of the absorbing layer 4 '' of the formation 2.

If the heights of the absorbing interlayers 4 'and 4' 'of formation 2 have a large run-up, for example, 1 m and 2.5 m, and the heights of clay impermeable layers 3', 3 '' and 3 '' ', for example, 0.8 m, which does not allow hermetically to cut off one or another interval of the absorbing interlayers of the formation from each other, then after the hydraulic fracturing of each interlayer, the device rises to the surface where the pipe of length L is replaced by a longer or shorter depending on the height of the next absorbing interlayers of the formation 2, after which the device descends to next underlying interval relative to the previous him for hydraulic fracturing.

After cutting off the absorbing layer of the formation into it through the tubing string 5, hydraulic fracturing fluid is injected for 3-4 hours under a pressure that is twice the injectivity pressure of the underground formation, for example, the injection pressure into the formation to maintain formation pressure is 18 MPa. Then the injection pressure of the fracturing fluid is 18 MPa × 2 = 36 MPa, and water, for example fresh water with a density of ρ = 1000-1050 kg / m ^{3, is} used as the fracturing fluid.

To do this, at the wellhead, the upper end of the tubing string is connected to the injection line of pumping units, for example, TsA-320, i.e. connected in series from two to four pumping units CA-320 and create the above pressure 36 MPa hydraulic fracturing fluid. In this case, it is necessary to sequentially connect two pumping units CA-320 in order to ensure injection of hydraulic fracturing fluid in the absorbing interlayer 4 'of formation 2 under a pressure of 36 MPa.

After that, two packers are unpacked and the tubing string 5 is lowered below (into the next interval of the absorbing layer of the formation) and the above operation is repeated again the required number of times depending on the number of absorbing layers in the formation, for example 4 times. Under a pressure of 36 MPa, natural cracks in the absorbing interlayers 4 '; 4 '' ... 4 '' of reservoir 2 is expanding and the absorption capacity of these absorbing interlayers is 4 '; 4 '' ... 4 '' increases dramatically.

Such an operation is a simplified version of hydraulic fracturing, after which an irreversible crack opening process takes place in the reservoir, through which suspension and clay sediments are driven deep into the reservoir. The flow rate of the injected fracturing fluid (water) usually increases faster than the discharge pressure, i.e. absorption coefficient increases with increasing discharge pressure.

In-depth studies by flowmeters have shown that this also increases the absorption interval, and consequently, the coverage of the formation by the process of displacement in thickness as a result of an increase in the opening of natural cracks and the addition of additional interlayers of the formation to the process of liquid absorption.

Next, all the absorbing interlayers of the formation are compacted by injection of a proppant slurry through the tubing string 5, a blank packer 7 (see Fig. 2) is installed under the lowest absorbing interlayer 4 '' of the formation 2 (see Fig. 2), for example, the TatNIPIneft design packer (patent RU No. 2259466. IPC 8 E21B 33/12, published in Bulletin No. 24 of 08/27/2005), and a passage packer 8, lowered onto the tubing string, for example, a passage through the PRO- NMO design NPF "Packer" (Oktyabrsky, Republic of Bashkortostan, Russia).

Further along the tubing string 5 simultaneously to all absorbing interlayers 4 '; 4 '' ... 4 '' formation 2 injected a hydraulic mixture with proppant, which is injected into the well from 3 to 6 m ^{3 of} lime suspension in a concentration of 20 kg CaO per 1 m ^{3 of} water, followed by addition in a ratio of 1: 0.2 up to 1: 0.4 sulfite-alcohol stillage (PRS) with a viscosity of 400-500-10 ^-3 Pa · s. Sulphite-alcohol stillage is a binder and improves the quality of proppant. Sulphite-alcohol bard is produced in accordance with TU 81-04-225-79. After that, the unpacker 8 is unpacked and removed from the well 1 together with the tubing string 5 from the well, and then by lowering the trap on the tubing string or on the rope (not shown in Figs. 1 and 2), the packer plug 7 is removed from the well 1. After that, injection well 1 is put into operation, i.e. start it up for injection, while water with a density of 1000-1180 kg / m, not containing a suspension and iron hydroxide, is used as a working agent injected into injection well 1.

With a subsequent increase in the discharge pressure by this technique, it is possible to expand the absorption interval and even out or expand the injectivity profile.

The method of hydraulic fracturing of a low-permeability reservoir of an injection well allows to increase the efficiency (up to 20-30%) of hydraulic fracturing in a low-permeable reservoir by conducting an interval fracturing of each permeable interlayer of a low-permeable reservoir, since during an interval hydraulic fracturing using fresh water as a fracturing fluid with a density ρ = 1000-1050 kg / m ³ , injected over several hours, a more effective effect is made on each absorbing interlayer due to their disconnection from each other and impermeable clay interlayers during hydraulic fracturing.

In addition, the proposed method allows to perform hydraulic fracturing in low-permeable formations, regardless of the injectivity of the formation and the rate of injection of hydraulic fracturing fluid into the formation during hydraulic fracturing, and subsequent use as a working agent (to maintain reservoir pressure), pumped into a freshwater injection well with a density of 1000 -1180 kg / m ^3, not containing iron hydroxide slurry and allows to increase the period of operation of the well injectivity loss to low permeability of the formation and, consequently, of replay s work to restore injectivity of the formation.

Claims (1)

Method of hydraulic fracturing of a low-permeable injection well, comprising pumping tubing through a well through a tubing string — tubing with a packer into a hydraulic fracturing fluid with a viscosity of less than 0.01 Pa · s, followed by pumping a hydraulic mixture with proppant, characterized in that the hydraulic fracturing is performed interval from top to bottom in each interlayer of the formation using two packers installed above and below the interval of the formation intended for hydraulic fracturing, injection is carried out into each absorbing interlayer of the formation through the tubing string the hydraulic fracturing fluid for 3-4 hours under pressure twice the injectivity pressure of the underground reservoir, the above operations are repeated depending on the number of absorbing interlayers of the formation, after which the installation of a blank packer under the lower absorbing interlayer and a through packer in the tubing string above the upper intercalation of the formation producing compaction of the absorbent layers of the formation by pumping the tubing string with proppant slurry as which is pumped into the well from 3 to 6 m ³ of limestone slurry in conc tion 20 kg CaO per 1 m ³ of water, followed by addition at a ratio of from 1: 0.2 to 1: 0.4 sulfite-alcohol stillage - PRS viscosity 450-500-10 ^-3 Pa · s, after which the injection well in the run operation, and as a working agent, injected into the injection well, use water with a density of 1000-1180 kg / m ³ not containing a suspension and iron hydroxide.

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